In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art.
Machining of workpieces of high strength materials and, particularly, large forged structural components formed of high strength materials, generally requires many hours to complete the machining to finished specifications. As a result of the large size of the finished components, long-reach material removal tools mounted in machine tools are used to perform the machining.
However, workpieces of high strength materials, such as, e.g., titanium, are difficult to machine, partially due to the “push back” force on the tools that is characteristic of machining many high strength materials. The combination of “push back” force and a long-reach (flexible) tool requires extra machine compensation to ensure that the material is adequately removed. In practice, up to 30% of the total time spent machining these workpieces is spent on spring-back passes, i.e., multiple passes over the same area of the workpiece being machined to clean up material left behind due to tool deflection and to reach final specifications.
It is well known that cemented carbide materials have a Young's modulus around twice that of steel. Attempts have been made to apply tools with cemented carbide shanks in the machining of workpieces of high strength materials. For example, FIG. 1 illustrates a material removal tool 10 with a unitary cemented carbide shank 12. The cemented carbide shank 12 extends from the mating end 14 of the material removal tool 10 toward the cutting end 16 of the material removal tool 10 and is formed of one piece. The cemented carbide shank 12 can have an internally arranged piece of steel, such as the steel rod 18 shown in FIG. 1. At the mating end 14 is a suitable mating surface 20 that mates with the base of the operating machine tool (not shown). At the cutting end 16 is a coupling 22 that at a first end 24 connects to the cemented carbide shank 12 and that at a second end 26 has a connector 28. Typically, a cap with mounted cutting inserts (not shown) is affixed to the connector 28.
The typical prior art material removal tool exhibits catastrophic breakage of the cemented carbide shank. Without being held to one theory of failure, it is believed that bending, e.g., deflection of the distal end, of the tools with unitary-shanks places a compressive load on one side of the shank and a tensile load on the other side of the shank. However, cemented carbide is generally fine grained (approximately 1 μm to 2 μm) and the crack mean free path is low, characteristics which generally facilitate crack propagation and failure. Thus, when under tensile forces the unitary-cemented carbide shank fails easily.
One non-limiting example of machining with long reach material removal tools where push back is observed is machining of large, single-piece, forged structural components formed from high strength materials, predominantly high strength materials like titanium. These structural components are used in the aerospace industry, such as for commercial aircraft, and are very expensive. For example, these structural components can be >$200,000 before any machining is performed, and generally, many hours are required to complete the machining to finished specifications. There is a large savings potential (machine time & tool expense) by minimizing tool deflections and the need for “spring back” passes.